Could Humans Cause Prairie Lake Food Webs to Collapse?
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Disturbed ecosystems are particularly vulnerable to top predator loss. Prediction of these losses remains challenging and controversial due to the importance of both community interactions and the tolerance of individual species. Here, we combined within-species biological indicators of a top predator (growth, physical condition and genetic diversity of walleye) with metrics of overall food-web structure (diversity and web complexity) to evaluate potential human causes of food-web disruption across 22 prairie lakes. In this study, food webs ranged from simple plankton communities to a complex community of fish, plankton, and invertebrates. Human disturbances included climate variability, land-use and fisheries activity. Both food-web structure and top predator health were primarily influenced by salinity, fertilizer runoff and gamefish stocking. Higher predator levels declined above 3 g/L salinity or 90 ug/L phophorus and showed physical stress below these levels. Ongoing attempts to maintain desirable fish communities through stocking were sometimes successful but often costly to the ecosystem. Future declines in community complexity are expected with climate change and new farming practices.